U.S.
President Donald Trump signs executive orders in the Hall of
Heroes at the Department of Defense on January 27, 2017 in
Arlington, VirginiaOlivier
Douliery-Pool/Getty Images

The White House may compel US customs officials and border
patrol agents to ask foreign visitors to provide their social
media and cell phone contacts upon entering the US, White
House policy director Stephen Millersaid onSaturday.

The move would fall under Trump's executive order temporarily
barring refugees and visa holders from six Muslim-majority
countries —Iraq, Iran, Sudan, Libya, Somalia and Yemen
— from entering the US, according to CNN.

Syrians have been banned indefinitely.

The idea of checking foreigners' social media posts, which
remains limited to a preliminary discussion, draws on a supposed
history of terror attacks where the attacker had previously
expressed extremist views on platforms like Facebook and Twitter.

Some have pointed to the San Bernardino terror attack as evidence
that such a policy might be useful: An FBI document produced
shortly after the shooting said that the woman who helped
carry it out
pledged allegiance to ISIS while the attack was ongoing. FBI
director James Comey later confirmed, however, that the attackers
— Syed Rizwan Farook, 28, and Tashfeen Malik, 29 —
expressed support for "jihad and martyrdom"
in private communications but never did so publicly on social
media.

It is unclear whether the social media mandate would be
constitutional. Legal challenges have already been presented to
Trump's "extreme vetting" order, and large protests erupted at
airports across the country on Saturday as news emerged that
people from the banned countries, who had valid visas and green
cards, were being detained — and, in some cases, deported —
by customs officials and border patrol agents.

Lawyers representing two Iraqi refugees who were
detained at John F. Kennedy airport in New York
filed legal challenges to Trump's executive order, and a federal judge in
Brooklyn issued
an emergency rulingSaturday evening to prevent the continued
deportation of travelers.

The ruling, a temporary emergency stay, now allows
those who landed in the US and hold a valid visa to
remain. Federal judges in Virginia,
Massachusetts, and Washington also made emergency rulings on
various aspects of the executive order.